The purpose of this project is to study the physical, chemical, and ultrastructural properties of calcium phosphate salts, and to clarify the kinetic and thermodynamic processes and the interactions with substances of biological interest that uniquely enable calcium phosphate salts to carry out their specialized role in vivo. The properties of calcium phosphate salts are being studied with a variety of ultrastructural and physical-chemical techniques such as spectroscopic methods, x-ray diffraction, surface area analyses, chromatographic and standard analytical chemistry procedures. Currently, the principal effort under this project is to study the physicochemical effects that biologically important anionic electrolytes have on the texture, i.e., size/shape, of apatite crystals grown in vitro under constant physiological-like solution conditions. The aim of this study is to distinguish the direct effect these solution substances have on the texture of biological apatites from that brought about by the metabolic and matrix changes these substances induce in vivo. Previous results from this study showed that secondary crystal proliferation rather than primary crystal growth was the dominant accretion mechanism in apatite precipitation reactions carried out in vitro in the presence of physiological levels of ionic calcium and phosphate. Solution carbonate was found to be the principal reason why the apatite formed by a proliferating mechanism, and may be a significant solution factor in controlling the size of apatite crystals in skeletal tissues. In our most recent studies, other anionic electrolytes were found to affect crystal size as well, though not to the same extent as carbonate. Their effect on size was dependent on how strongly they inhibited accretion kinetics. Serum albumen and citrate, the two weakest of the inhibitory substances examined, further limited primary growth of the apatite crystals, principally by suppressing increases in width and thickness. In contrast, stronger inhibitors such as bisphosphonates, polycarboxylates, and the polyphosphorylated protein, phosvitin partially reversed the suppressive effect that carbonate had on primary crystal growth by stimulating increases in width and thickness. Interestingly, none of these inhibitors had a significant effect on growth in crystal length. These data suggest that polyanions in the extravascular fluid phase in skeletal tissues may have a collateral role in controlling the size of apatite crystals in these tissues through direct anion-mineral interactions on the lateral surfaces of these crystals. - Apatite,Calcification,Calcium phosphates,Carbonate,Crystal growth,Mineralization